Tight beam position controlling apparatus

Abstract

A light beam position controlling apparatus includes a linear motor for driving an optical head in the radial direction of an optical disk, a radial actuator built-in within said optical head and adapted to drive an objective lens for causing the light beam to be accurately positioned in the radial direction of the optical disk and to rotate a mirror for causing the light beam to be deflected in the radial direction of the optical disk, which can be improved in the compression factor of the servo performance, by providing a phase lag compensation circuit and a damping correction circuit for increasing the gain of the transfer function at the resonance frequency of both the linear motor and radial actuator.

What is claimed is: 
     
       1. A light beam position controlling apparatus comprising: actuator means for performing a focus controlling operation or a radial controlling operation;   a phase lag compensating circuit wherein a transfer function is ##EQU69##  wherein w 1 , w 2  are two break point frequencies where S=jw and w 2  is larger than w 1  ;   a damping correction circuit wherein a transfer function is ##EQU70##  wherein ζ 1  is a damping factor, ζ 0  is a damping factor of said actuator means; and   a driving circuit for driving said actuator upon receiving a driving current obtained with phase lag compensation and damping correction after an error signal is passed through said phase lag compensating circuit and damping correction circuit, the resonance frequency and damping factor of said actuator being respectively, w 0  and ζ 0 , ζ 0  being smaller than 1.   
     
     
       2. The apparatus as defined in claim 1, wherein said phase lag compensating circuit is constructed in condition of ω 1  ·ω 2  =ω 0   2 , and said damping correction circuit is construed in condition of ##EQU71## 
     
     
       3. The apparatus as defined in claim 2, wherein the resonance frequency of said damping correction circuit is set to be lower than the resonance frequency ω 0  of said actuator. 
     
     
       4. The apparatus as defined in claim 1, wherein the resonance frequency of said damping correction circuit is set to be lower than the resonance frequency ω 0  of said actuator. 
     
     
       5. A light beam position controlling apparatus comprising: a radial actuator adapted to drive an objective lens for causing the light beam to be accurately positioned in the radial direction of an optical disk;   a band-pass filter providing a driving current of said radial actuator, wherein the rotation frequency w r  of the optical disk is approximately a central frequency of said filter;   memory means for storing said driving current in synchronous relation with the optical disk rotation, said stored current being fed into said radial actuator.   
     
     
       6. A light beam position controlling apparatus comprising: a linear motor for driving an optical head in the radial direction of an optical disk;   a radial actuator built-in within said optical head and adapted to drive an objective lens, for causing the light beam to be accurately positioned in the radial direction in the optical disk and to rotate a mirror for causing the light beam to be deflected in the radial direction of the optical disk;   a band-pass filter, wherein the driving current of said linear motor is flowed through said band-pass filter wherein the central frequency is approximately the rotation frequency w r  of the optical disk; and   memory means for storing said driving current in synchronous relation with the optical disk rotation, said stored current being fed into said linear motor.   
     
     
       7. A light beam position controlling apparatus comprising: a linear motor for driving an optical head in the radial direction of an optical disk;   circuit means for setting the resonance frequency w L  of said linear motor to at least the rotation frequency w r  of the disk;   means for controlling said linear motor including compensating circuit means for giving to said controlling means a phase lag compensation which raises the gain of a frequency band of said controlling means including the resonance frequency.   
     
     
       8. A light beam position controlling apparatus comprising: a linear motor for driving an optical head in the radial direction of an optical disk;   a radial actuator built-in within said optical head and adapted to drive an objective lens, for causing the light beam to be accurately positioned in the radial direction of the optical disk and for rotating and driving a mirror, for causing the light beam to be deflected in the radial direction of the optical disk, wherein a resonance frequency w L  of said linear motor is equal to at least the rotation frequency w r  of the disk; and   means for controlling said linear motor including compensating circuit means for giving to said controlling means a phase lag compensation which raises the gain of a frequency band of said controlling means including the resonance frequency.   
     
     
       9. A light beam position controlling apparatus, comprising: a linear motor for driving an optical head in the radial direction of an optical disk;   a radial actuator built-in to said optical head and adapted to drive an objective lens for causing said light beam to be accurately positioned in the radial direction of said optical disk, and to rotate a mirror for causing said light beam to be deflected in the radial direction of said optical disk;   a band-pass filter with a center frequency approximately equal to a resonance frequency of said linear motor for adding a control current of said linear motor to a control current of said radial actuator;   wherein the ratio between the low-frequency gain of a feedback transfer function of said linear motor and the low-frequency gain of a feedback transfer function of said radial actuator is approximately equal to the square of the ratio between the resonance frequency of said radial actuator and the resonance frequency of said linear motor.   
     
     
       10. The light beam position controlling apparatus of claim 9, wherein the control current of said radial actuator first passes through a damping correction circuit having a transfer function corresponding to ##EQU72## wherein S=jw, w R  =the resonance frequency of said radial actuator, ζ R  =the damping factor of said radial actuator, ζ R  '≧1, and the control current of said linear motor first passes through a damping correction circuit having a transfer function corresponding to ##EQU73## wherein ζ L  =the damping factor of said linear motor, w L  =the resonance frequency of said linear motor, and ζ L  '>1.